The present invention relates to making stain- or dye-resistant polyamide carpet fibers by reducing the amino end group content of the polyamide. The present invention also relates to reducing the rate of monomer regeneration during extrusion of the polyamide by reducing the amount of end groups in the polyamide.
As used herein, the term xe2x80x9cfiberxe2x80x9d includes fibers of extreme or indefinite length (i.e., filaments) and fibers of short length (i.e., staple fibers). The term xe2x80x9cyarnxe2x80x9d as used herein means a continuous strand of fibers.
The terms xe2x80x9cstainxe2x80x9d and xe2x80x9cstainingxe2x80x9d as used herein with reference to polyamide fibers mean discoloration of such fibers caused by a chemical or physical attraction thereof with a substance such as, for example, food red. The terms xe2x80x9cstain-resistantxe2x80x9d and xe2x80x9cstain resistancexe2x80x9d as used herein with respect to polyamide fibers or carpets refers to the ability of the fiber or carpet to resist staining.
As used herein, xe2x80x9cunmodified polyamidexe2x80x9d refers to a typical commercially available polyamide with an AEG above 20 meq/kg that is known in the art such as, for example, nylon 6 or nylon 6,6.
Polyamide fibers are relatively inexpensive and offer a desirable combination of qualities such as durability, comfort, and ease of manufacture into a broad range of colors, patterns, and textures. As a result, polyamide fibers are widely used in the home and industry as carpets, drapery material, upholstery, and clothing. Carpets made from polyamide fibers are a popular floor covering for residential and commercial applications.
Polyamide fibers dye easily with acid dyes. Consequently, carpets made from polyamide fibers stain easily when exposed to natural or artificial acid dyes that exist in some foods, drinks, medicines, and other consumer products. The resulting stains cannot be easily removed under ordinary cleaning conditions. The severe staining of carpeting is a major problem for consumers. In fact, surveys show that more carpets are replaced because of staining than because of wear. Accordingly, it is desirable to provide polyamide fibers that resist common household stains, thereby increasing the life of the carpet.
One way of avoiding such staining is to topically apply to the surface of the polyamide filaments materials that function as stain blockers so as to prevent acid stains from permanently coloring the yarn. Topical treatments may be sulfonated materials that act as xe2x80x9ccolorless dyesxe2x80x9d and bind the amine dye sites on the polyamide polymer. Sulfonated products for topical application to polyamide substrates are described in, for example, U.S. Pat. No. 4,963,409 to Liss et al., U.S. Pat. No. 5,223,340 to Moss, III et al., U.S. Pat. No. 5,316,850 to Sargent et al., and U.S. Pat. No. 5,436,049 to Hu. Topical treatments, however, tend to be costly and non-permanent (wash away with one or more shampoos).
Another way to make stain- or dye-resistant polyamide carpet fibers is to reduce the number of amino end groups in the polyamide yarn. Methods have been developed to reduce the amino end group content of polyamide fibers by adding amino end group blockers such as caprolactone and butyrolactone to the extruder during polymer extrusion. Blocking the end groups during polymer production greatly reduces the rate of polymerization, and the obtainable amino end group level would still be too high to provide meaningful stain resistance.
There remains a need for stain- or dye-resistant polyamide carpet fibers that overcome the above-discussed limitations, as well as a simpler and more economical process for producing the same.
Moreover, during extrusion, polyamides regenerate the starting monomers via the end groups in the melt. The regenerated monomers are deposited on the extruder die, which causes fuming and other processing problems. The regenerated monomers also show up in the finished products.
A need exists, therefore, for a method of reducing the rate of regeneration of starting monomers from polyamides during extrusion.
It is an object of the present invention to provide stain- or dye-resistant polyamide carpet fibers.
It is also an object of the present invention to produce a polyamide polymer that significantly slows down the rate of monomer regeneration during extrusion or remelting.
It has now been found that these objects may be achieved by reducing the number of end groups of solid state polyamide with an acid, anhydride, or amine gas.
The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments thereof.
To promote an understanding of the principles of the present invention, descriptions of specific embodiments of the invention follow, and specific language is used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is intended by the use of this specific language and that alterations, modifications, equivalents, and further applications of the principles of the invention discussed are contemplated as would normally occur to one of ordinary skill in the art to which the invention pertains.
According to the present invention there is provided a method of processing solid-state polyamide comprising treating said polyamide with gas-phase acid, anhydride, or amine.
According to the present invention there is also provided a method of reducing the amino end group content of polyamide comprising treating said polyamide with gas-phase acid or anhydride. The polyamide treated in accordance with the present invention is particularly advantageous for solution-dyed fibers, greatly reducing the staining propensity of such carpets.
To reduce the number of amino end groups, solid state polyamide may be treated with an inert carrier gas such as nitrogen or argon containing acid or anhydride at temperatures above the boiling point of the acid or anhydride. The polyamide reacts in the solid state with the acid or anhydride in the gas phase at temperatures elevated above room temperature to reduce the number of amino end groups in the polyamide. Suitable acids include acetic acid, formic acid, and propionic acid. Acetic acid and formic acid are the preferred acids. Suitable anhydrides include acetic anhydride, maleic anhydride, and propionic anhydride. Acetic anhydride is the preferred anhydride.
Further according to the present invention there is provided a method of reducing the carboxylic end group content of polyamide comprising treating said polyamide with gas-phase amine. Reducing the carboxylic end group content reduces both the rate of monomer regeneration during extrusion and the amount of regenerated monomers in the finished products.
To reduce the number of carboxylic end groups, solid state polyamide may be treated with amines that are in the gas phase. More particularly, the polyamide is treated with a gas phase amine at temperatures above its boiling point such that the amine reacts with the polyamide to reduce the number of carboxylic end groups in the polyamide. Suitable amines include ammonia; methyl amine; dimethyl amine; ethyl amine; propylamine; 2-propylamine; butylamine; sec-butylamine; tert-butylamine; pentylamine; 2-pentylamine; 3-pentylamine; hexylamine; 2-hexylamine; 3-hexylamine, heptylamine; 2-heptylamine; 3-heptylamine; 4-heptylamine; octylamine; 2-octylamine; 3-octylamine; cyclopropylamine; cyclobutylamine; cyclohexylamine; cycloheptylamine; cyclooctylamine; 1,1,3,3-tetramethylbutylamine; diethylamine; diproylamine; dibytylamine;di-sec-butylamine; dipetylamine; N-ethylmethylamine; N-ethylpropylamine; N-ethylpropylamine; 1,2-diaminopropane; 1,3-diaminopropane; 1,2-diaminobutane; 1,3-diaminobutane; and 1,4-diaminobutane. Preferred amines are ammonia, methyl amine, and dimethyl amine.
Polyamides suitable for use in the invention are those that are generically known by the term xe2x80x9cnylonxe2x80x9d and that are long chain synthetic polymers containing amide (xe2x80x94COxe2x80x94NHxe2x80x94) linkages along the main polymer chain. Examples of such polyamides include homopolyamides and copolyamides that are obtained by the polymerization of lactam or aminocaprionic acid, as well as a copolymerization product from mixtures of diamines and dicarboxylic acids or lactams.
Typical polyamides include nylon 6 [poly(epsilon-caprolactam)], nylon 6/6 (polyhexamethylene adipamide), nylon 6/9, nylon 6/10, nylon 6T, nylon 6/12, nylon 11, nylon 12, nylon 4/6, and copolymers or mixtures thereof. Polyamides can also be copolymers of nylon 6 or nylon 6/6 and a nylon salt obtained by reacting a dicarboxylic acid component such as terephthalic acid, isophthalic acid, adipic acid, or sebacic acid with a diamine such as hexamethylene diamine, methaxylene diamine, or 1,4-bisaminomethylcyclohexane. Preferred polyamides are nylon 6 and nylon 6/6. Nylon 6 is most preferred.
The polyamide treated according to the present invention may be formed into various articles. Non-limiting examples of such articles include fibers, yarns, textile fabrics, and the like.
Fibers may be formed by subjecting the modified polyamide of the present invention to any conventional fiber-forming process such as, for example, that disclosed in U.S. Pat. Nos. 4,983,448 to Karageorgiou and 5,487,860 to Kent et al., both of which are incorporated herein by reference.
Carpet may be made using conventional carpet-making techniques such as weaving or tufting the fibers into a backing material and binding the fibers to the backing with latex or other adhesives. The carpet may be cut-pile, berber, unlevel loop, level loop, or any other style according to the popular fashion. If desired, the carpet may be in the form of carpet tiles, with or without foam backing. By way of example, in the case of cut-pile carpeting, the yarn is tufted into a primary backing and cut to form cut-pile carpeting. The primary backing material may be woven or nonwoven jute, nylon, polyester, polypropylene, etc. The cut-pile carpeting is dyed to the desired shade. The primary backing is then coated with a suitable latex material such as a conventional styrene-butadiene (xe2x80x9cSBxe2x80x9d) latex, vinylidene chloride polymer, or vinyl chloride-vinylidene chloride copolymers. It is common practice to use fillers such as calcium carbonate to reduce latex costs. The final step is to apply a secondary carpet backing to the latex-based adhesive. The secondary backing may be jute, polypropylene, nylon, polyester, etc. The carpet may be foam backed or not. The carpet of the present invention can be a variety of pile weights, pile heights, and styles. There is not currently believed to be any limitation on the carpet style.
Additionally, the fibers may be dyed or colored utilizing conventional fiber-coloring techniques. For example, the fibers of this invention may be subjected to an acid dye bath to achieve desired fiber coloration. Alternatively, the polyamide may be colored in the melt prior to fiber formation (i.e., solution dyed) using conventional pigments for such purpose.
The invention will be further described by reference to the following detailed examples. The examples are set forth by way of illustration and are not intended to limit the scope of the invention. All percentages are percentages by weight unless otherwise noted. In the following examples, the test procedures described below are used to measure the stated properties.
The amino end group content is determined by dissolving about 2.0 g of the polymer in about 60 ml of a phenol-methanol mixture (68:32). This solution is titrated with about 0.20 normal HCl at about 25xc2x0 C. by a potentiometric method, wherein the endpoint is determined by a steep potential increase.
The carboxylic end group content is determined by dissolving 0.30 g of the polymer in about 40 ml of benzyl alcohol at 180xc2x0 C. The solution is titrated with about 0.03 normal t-butyl ammonium hydroxide at 80xc2x0 C. to about 1000xc2x0 C. by a potentiometric method, wherein the endpoint is determined by a steep potential increase.